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The last thing any pregnant woman wants to hear is that there's one more thing she should give up. But a study published in The American Journal of Obstetrics and Gynecology found expecting mothers should monitor their caffeine intake, especially in early pregnancy.

The study followed more than 1,000 women throughout their pregnancies and found a substantial link between caffeine in early pregnancy and miscarriage rates. This wasn't the first study to find such a link, but it is getting more attention than past research.

According to head researcher Dr. De-Kun Li, pregnant women who consume as little as 200 milligrams of caffeine per day can double their risk of miscarriage. What does this look like in your coffee mug? It depends on how you brew your java, but it's not a lot. Starbucks' smallest coffee–a tall–contains 300 milligrams of caffeine.

Why caffeine in early pregnancy can be risky

The San Francisco-based study found that caffeine in early pregnancy might be dangerous to the developing fetus because it crosses the placenta. A fetus does not have a sufficient metabolic system to cope with the increase in heart rate that results from this jolt of caffeine. In severe cases, the result can be a spontaneous abortion. In less severe cases, caffeine can contribute to low birth weight. Because the risk of miscarriage is highest in the first three or four months, caffeine intake should be most strictly monitored during early pregnancy.